Generally, when a flat cable (hereinafter referred to as “flexible flat cable (FFC)”) obtained by sandwiching a plurality of flat conductors arranged in parallel in a width direction in a sheet-like insulating covering and a plurality of insulated wires each obtained by covering a conductor with an insulating covering are connected, the conductor of each insulated wire is connected to each flat conductor of the flat cable via a connection terminal called a wire-to-FFC joint (WF) terminal.
Thus, for one FFC, the number of insulated wires and connection terminals needs to be the same as the number of flat conductors of the FFC, and the insulated wires and connection terminals are arranged in parallel in the width direction of the FFC.
A connection portion that uses such a connection terminal of the FFC and insulated wire requires waterproofing properties for preventing water penetration, for example. Patent Document 1, for example, proposes a structure in which connection terminals arranged in parallel in the width direction are arranged as a whole in a protective case that extends across an end portion of the FFC and an end portion of the insulated wire and has an open upper surface, and a sealing material serving as a filler is filled in the protective case.
However, such a connection structure with waterproofing properties requires materials and processes such as disposing the connection terminals in the protective case and filling the protective case with a sealing material such as a hot melt material, making the structure inadequate in terms of desires for further improving manufacturing efficiency and achieving reductions in cost.